Please help with Atom composition

A. 35Cl-

Explanation:

According to the electron for diagram attached to this question, a neutral chlorine atom i.e with a charge of 0, is shown to contain 7 valence electrons in its outermost shell. This means that in order for chlorine to have a stable arrangement of eight valence electrons, it must gain one more electron.

Gaining one more electron, for a neutral chlorine atom, means that it now becomes an atom with one negative charge i.e. an anion (Cl-). Therefore, based on the attached diagram, the symbol "35Cl-" shows a chlorine atom that have a stable arrangement of eight valence electrons.